The present invention relates to an image reading device installed in a copier, facsimile apparatus or similar image forming apparatus and, more particularly, to a device for reading the images of a book document and having a page turning capability.
An automatic document feeder (ADF) is extensively used with an image forming apparatus of the kind described as an image reading device. The ADF automatically transports a sheet document to a reading position, reads the image of the document, and then discharges the document from the reading device. So far as the document is a sheet document, the ADF can read it automatically. However, regarding a book document, it is extremely difficult to automate the page turning operation of the ADF. The only measure left at the present stage of development is to turn the pages of a book manually. Although various methods and means have, of course, been proposed for reading a book document automatically, most of them are merely conceptual and far from practicality.
In the light of this, Japanese Patent Laid-Open Publication (Kokai) No. 2-193589 discloses a device capable of reading a book document while turning the pages thereof with a page turning and reading unit, or scanning unit as referred to hereinafter. The scanning unit has thereinside page receiving means, page attracting means, page separating means, reading means, etc. Specifically, the scanning unit has a page turning belt extending along the surface of a document table. While a document is laid on the document table in a spread position between the surface of the table and the belt, the scanning unit is moved relative to the document while causing the belt to form a roundabout portion moving away from the table. With this kind of device, it is possible to fully automate the page turning and image reading operation which has heretofore been time- and labor consuming and, therefore, to implement a multifunction image reading system remarkably enhancing the productivity of, for example, a copier.
Assume that in the conventional device the page turning means for turning the pages of a book document in contact with the spread surface thereof is constituted by a dielectric belt, and means for generating an electric field on the belt. Then, the prerequisite is that the belt be capable of surely causing the page of the document to adhere thereto. Another prerequisite is that only the top leaf of the book adheres to the belt.
Further, assume that the dielectric belt, constituting the page turning means in combination with the electric field generating means, is movable upward while carrying the top page of the document therewith, thereby separating the top page from the underlying pages. In this case, it is necessary to stabilize the movement of the scanning unit and prevent the leaves of the book from being torn or bent in the event of page turning. Particularly, the top page fully turned by the belt should be smoothly released.
Moreover, with the page turning means constituted by the dielectric belt and electric field generating means, it is necessary that a high voltage harness for feeding a high voltage to the electric field generating means be wired safely, and the wasteful application of a high voltage to the belt be minimized which would cause the belt to deteriorate due to fatigue.